1. Field of the Invention
This invention relates to an optical element and a method for making the same, more particularly to an optical element and a method involving forming a resin layer with a plurality of adjoining protrusions using a press-molding plate for making the optical element.
2. Description of the Related Art
A backlight module is one of the key components for making a liquid crystal display, and serves to provide a uniform light source for enabling the display of an image on a liquid crystal panel. Based on the disposition of the light source, backlight modules can be classified into a bottom lighting type and a side lighting type. The side lighting type normally includes a light guide and optical elements, such as diffusing sheets and brightness-enhancing sheets, for transforming the light emerging from the light guide into a uniform light to be cast onto a liquid crystal panel. The bottom lighting type normally includes a diffuser plate and optical elements, such as diffusing sheets and brightness-enhancing sheets, for enhancing the uniformity and brightness of the light emerging from the diffuser plate.
FIG. 1 illustrates a conventional optical element 1 for a bottom lighting type backlight module. The conventional optical element 1 includes a diffuser plate 11 and a plurality of spaced apart protrusions 12 formed on the diffuser plate 11 for concentrating the light emerging from the diffuser plate 11. In order to smoothen the light concentrated by the protrusions 12, the top surface 121 of each of the protrusions 12 is curved.
Manufacture of the optical element 1 involves the steps of: preparing the diffuser plate 11; coating a curable resin on the diffuser plate 11 so as to form a curable resin layer; curing and hardening the curable resin layer using a UV light or an E-beam; patterning and etching the hardened resin layer so as to form the protrusions 12; and heating and softening the protrusions 12 so as to form the curved top surface 121 of each of the protrusions 12. The softening temperature depends on the material of the curable resin, and is about 55° C. for epoxy resin or acrylic resin.
However, since the protrusions 12 are spaced apart from each other, a portion of the light emerging from the diffuser plate 11 passes through the protrusions 12, and the remainder of the light by-passes the protrusions 12. As a consequence, the light passing through the protrusions 12 and the light by-passing the protrusions 12 differ in intensity and direction, which results in a non-uniform light beam when projected onto an adjacent optical component.